1. Field of the Invention
The present invention relates to a bearing device, a spindle motor provided with the bearing device, and a disk drive apparatus provided with the spindle motor.
2. Description of the Related Art
A hard disk drive or an optical disk drive is typically equipped with a spindle motor arranged to rotate a disk about a central axis. The spindle motor includes a stator unit fixed to a housing of the device and a rotor unit arranged to hold a disk and rotate together with the disk. In the spindle motor, torque acting about the central axis of the spindle motor is generated by the magnetic flux generated between the stator unit and the rotor unit to thereby rotate the rotor unit with respect to the stator unit.
The stator unit and the rotor unit of the spindle motor are coupled together through a bearing device. A bearing device of the type including a substantially cylindrical sleeve surrounding the outer circumferential surface of a shaft and a substantially disk-shaped thrust plate making contact with the lower end portion of the shaft is one example of a conventionally known bearing device. In a bearing device of this type, the shaft is rotated about its central axis within the sleeve while being axially supported with the lower end portion thereof remaining in contact with the upper surface of the thrust plate.
The bearing device of this type enjoys an advantage in that it has a reduced number of component parts and is cost-effective. However, in this bearing device, friction occurs between the lower end portion of the shaft and the upper surface of the thrust plate during rotation of the shaft. This poses a problem in that a loss of torque is caused by the friction. There is also a fear that the thrust plate may be deformed when a load acting toward the thrust plate is applied to the shaft.
In particular, spindle motors for a hard disk drive require increased performance in terms of durability, reliability, noise reduction, power saving, rotation accuracy and so forth. To comply with these requirements, it is desirable to reduce the frictional losses in bearing devices used in spindle motors while also enhancing the load and impact resistances thereof.